Earphones are commonly used with a variety of electronic devices to provide mobile and/or personal access to audio content. For example, earphones can be used with music players, such as MP3 and CD players. Earphones can also be used with cellular phones, personal digital assistants, computers, and most other types of electronic devices that produce audio signals. However, the acoustic performance of the conventional earphones at different frequency, such as, low frequency, middle frequency, and high frequency are not tunable.